Switchable electrochromic devices with uniform switching and preferential area shading

ABSTRACT

A method for providing preferential coloring to a portion of an electrochromic window assembly, includes the steps of providing an electrochromic window assembly comprising first and second spaced apart transparent substrates defining a chamber therebetween, the first transparent substrate having a first conductive coating and the second transparent substrate having a second conductive coating, the chamber containing an electrochromic medium capable of coloring upon application of electrical potential thereto to provide reduced luminous transmittance; electrically connecting a plurality of first spaced facilities to the first conductive coating for providing the electrical potential to the first conductive coating; electrically connecting a plurality of second spaced facilities to the second conductive coating for providing the electrical potential to the second conductive coating; and applying an electrical current to selected ones of the plurality of first spaced facilities and to selected ones of the plurality of second spaced facilities to establish the electrical potential through a selected portion of the electrochromic medium such that the selected portion changes color and reduces its luminous transmittance.

CROSS REFERENCE TO RELATED PATENT APPLICATION

[0001] This patent application is a divisional of U.S. patentapplication Ser. No. 09/919,151, filed Jul. 31, 2001.

[0002] The present invention relates to switchable electrochromicdevices that are capable of uniform switching throughout the entirestructure and of preferential switching to selected areas. Moreparticularly, the present invention is directed to switchableelectrochromic devices, particularly large scale window transparenciesand window transparencies of non-uniform shape, which can uniformlyswitch from an activated to an unactivated state, and which cansimultaneously include both an activated area and an unactivated area.

[0003] Commercial electrochromic devices are well known in the art foruse as mirrors in motor vehicles. The patent literature also discussesuses of flat types of electrochromic devices for automotive windows,aircraft window assemblies, sunroofs, skylights, and architecturalwindows. Such electrochromic devices typically include a sealed chamberdefined by two pieces of glass that are separated by a gap or space thatcontains an electrochromic medium. The electrochromic medium typicallyincludes anodic compounds and cathodic compounds together in a solution.The glass substrates typically include transparent conductive layerscoated on facing surfaces of the glass and in contact with theelectrochromic medium.

[0004] The conductive layers on both glass substrates are connected toelectronic circuitry. When the conductive layers are electricallyenergized, an applied potential is introduced into the chamber of thedevice, which electrically energizes the electrochromic medium andcauses the medium to change color. For example, when the electrochromicmedium is energized, it can darken and begin to absorb light. For theelectrochromic rear-view mirror assemblies for motor vehicles, aphotocell can be incorporated into the electrochromic cell to detect achange in light reflected by the mirror and activate the electricalpotential to dim the mirror.

[0005] In the other proposed applications of electrochromic devices,various problems become prevalent as the size of the electrochromicdevice is enlarged. For instance, rear-view mirror assemblies involvesmall-scale electrochromic assemblies, typically about 2 inches by 10inches (5.08 cm to 25.4 cm) in size. In such electrochromic devices, ananodic bus bar is typically arranged at the top portion of the mirrorassembly, and a cathodic bus bar is typically arranged at the bottomportion of the mirror assembly.

[0006] Automotive windows, architectural windows, and some aircraftwindows on the other hand, are much larger in scale. As a result,switching between the lightened and darkened state in an electrochromicrear-view mirror assembly is typically quick and uniform, whereasswitching between the lightened and darkened state in a larger scaleelectrochromic device can be slow and non-uniform. Gradual, non-uniformcoloring or switching is a common problem associated with larger scaleelectrochromic window assemblies, commonly referred to as the “iriseffect”. This effect is typically due to the potential drop across thesurface of the transparent conductive coatings present on the surfacesof the substrates, which results in the applied potential being highestadjacent to the bus bars along the edge of the surface coating andlowest at the center of the cell as the electrical current passesthrough the electrochromic solution. Accordingly, the electrochromicmedium will typically display non-uniform coloring by initially coloringthe perimeter of the cell where the bus bars are located, i.e., closestto the point where the applied potential comes in contact withelectrochromic medium, and thereafter coloring toward the center of thecell. Traditionally, conductive films having high sheet resistance areused. However, such high sheet resistance films require higher voltagesand longer time periods to switch. Moreover, in conventionalelectrochromic devices, the entire assembly is shaded upon applicationof electrical potential.

[0007] Various attempts have been made to provide more uniform coloringof electrochromic devices to eliminate this iris effect. For example,various electrochromic chemical solutions have been chemically alteredto increase uniform coloring.

[0008] A need exists for electrochromic devices that are capable of moreuniform switching and coloring, can be easily manufactured and canoptionally include preferential areas of shading.

[0009] The present invention provides an electrochromic window assemblycomprising: a first transparent substrate including a first conductivecoating on a surface thereof; a second transparent substrate including asecond conductive coating on a surface thereof, the first transparentsubstrate and the second transparent substrate being spaced from eachother to define a chamber therebetween; an electrochromic mediumcontained in the chamber, the electrochromic medium having a luminoustransmittance that varies upon application of an electrical potentialthrough the electrochromic medium; a plurality of first spacedfacilities contacting the first conductive coating and capable ofdelivering electrical current to the first conductive coating; and aplurality of second spaced facilities contacting the second conductivecoating and capable of delivering electrical current to the secondconductive coating to establish the electrical potential through theelectrochromic medium. In one nonlimiting embodiment of the invention,the plurality of first spaced facilities and the plurality of secondspaced facilities are bus bars arranged about the perimeter of thewindow assembly. In another nonlimiting embodiment, the window assemblyfurther comprises a controller capable of controlling delivery ofelectrical current to selected ones of the plurality of first spacedfacilities and selected ones of the plurality of second spacedfacilities, such that the luminous transmittance through a first portionof the electrochromic medium is different from the luminoustransmittance through a second portion of the electrochromic medium.

[0010] The present invention also provides a method for providinguniform coloring to an electrochromic window assembly comprising:providing an electrochromic window assembly comprising first and secondspaced apart transparent substrates defining a chamber therebetween, thefirst transparent substrate having a first conductive coating and thesecond transparent substrate having a second conductive coating, thechamber containing an electrochromic medium capable of coloring uponapplication of electrical potential thereto to provide reduced luminoustransmittance; and applying an electrical current to opposing ends ofthe first conductive coating and to opposing ends of the secondconductive coating to establish the electrical potential through theelectrochromic medium, the opposing ends of the first conductive coatingand the second conductive coating being spaced from each other, whereinthe coloring of the electrochromic medium is uniform.

[0011] The present invention further provides a method for providingpreferential coloring to a portion of an electrochromic window assembly,comprising: providing an electrochromic window assembly comprising firstand second spaced apart transparent substrates defining a chambertherebetween, the first transparent substrate having a first conductivecoating and the second transparent substrate having a second conductivecoating, the chamber containing an electrochromic medium capable ofcoloring upon application of electrical potential thereto to providereduced luminous transmittance; electrically connecting a plurality offirst spaced facilities to the first conductive coating for providingthe electrical potential to the first conductive coating; electricallyconnecting a plurality of second spaced facilities to the secondconductive coating for providing the electrical potential to the secondconductive coating; applying an electrical current to selected ones ofthe plurality of first spaced facilities and to selected ones of theplurality of second spaced facilities to establish the electricalpotential through a selected portion of the electrochromic medium suchthat the selected portion changes color and reduces its luminoustransmittance.

[0012] The foregoing summary, as well as the following detaileddescription of embodiments of the invention, will be better understoodwhen read in conjunction with the appended drawings. In the drawings:

[0013]FIG. 1 is a perspective view of an embodiment of an electrochromicwindow assembly incorporating features to the present invention, withportions removed for clarity.

[0014]FIG. 2 is a front view of the electrochromic window assembly shownin FIG. 1.

[0015]FIG. 3 is a sectional view of the electrochromic window assemblytaken along line 3-3 of FIG. 2.

[0016]FIG. 4 is a perspective view of an alternate embodiment of anelectrochromic window assembly incorporating features of the presentinvention, having an oval-shaped geometry, for example, for use as anaircraft cabin window.

[0017]FIG. 5 is a front view of the electrochromic window assembly shownin FIG. 4.

[0018]FIG. 6 is a perspective view of an electrochromic window assemblyincorporating features of the present invention useful, for example, asan automobile windshield, automobile sunroof, or architectural glazing.

[0019]FIG. 7 is a front view of the electrochromic window assembly shownin FIG. 6.

[0020]FIG. 8 is a perspective view of an alternate embodiment of anelectrochromic window assembly incorporating features of the presentinvention and having a non-symmetrical geometry useful, for example, asan automobile sidelite or aircraft cockpit window.

[0021]FIG. 9 is a front view of the electrochromic window assembly asshown in FIG. 8.

[0022]FIG. 10 illustrates one embodiment of electrical circuitry usefulin connection with the present invention.

[0023]FIG. 11 is a front view of an electrochromic window assemblysimilar to the assembly shown in FIG. 8 that was used for testing.

[0024] The present invention is directed to single compartmentelectrochromic window assemblies having uniform switching or coloring,and which are capable of graded shading (i.e. a gradient shading) orpreferentially colored areas. In one nonlimiting embodiment of theinvention, the electrochromic window assembly includes a firsttransparent substrate coated with a first electrically conductivecoating and a second transparent substrate coated with a secondelectrically conductive coating. The first and second transparentsubstrates are spaced from each other to define a chamber therebetween,with the first and second conductive coatings facing each other. Anelectrochromic medium, which is capable of reduced light transmittanceupon application of an electrical potential through the medium, iscontained within the chamber. A plurality of first spaced facilities isfurther provided in contact with the first conductive coating, e.g.along opposing ends of the first substrate, for providing electricalcurrent thereto, and a plurality of second spaced facilities is providedin contact with the second conductive coating, e.g. along opposing endsof the second substrate, for providing electrical current thereto. Whencurrent from a DC power source is applied to the first plurality andsecond plurality of facilities, an electrical potential is impressedbetween the coatings and through the electrochromic medium such that theelectrochromic medium rapidly and uniformly colors to the desired color,due to the arrangement of the facilities. Moreover, the current can beapplied to selected ones of the first and second plurality of facilitiesand shorted to other selected ones of the first and second plurality offacilities, thereby producing a window assembly including a shaded areain a selected portion of the assembly.

[0025] For the purposes of this specification, unless otherwiseindicated, all numbers expressing quantities such as dimensions,voltages, luminous transmittance, performance measurements and so forthused in the specification and claims are to be understood as beingmodified in all instances by the term “about.” Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that canvary depending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

[0026] Notwithstanding that the numerical ranges and parameters settingforth the broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

[0027] In the following description, like elements bear like referencenumerals. Referring to FIGS. 1-3, electrochromic window assembly 10 isdepicted. Although not required, in one particular nonlimitingembodiment of the present invention, electrochromic window assembly 10has a generally symmetrical geometry. For example, electrochromic windowassembly 10 can be a square or rectangular shaped window assembly. Suchsymmetrical shaped window assemblies are particularly useful asarchitectural glazings, such as windows for buildings. The size andshape of electrochromic window assembly 10 can be selected according tothe particular desired use of the assembly.

[0028] Electrochromic window assembly 10 includes first transparentsubstrate 20 and second transparent substrate 30. Such substrates can bemade of any material known in the art for use in electrochromic devices,such as but not limited to polymeric materials, glass, metal, and thelike, and combinations of such materials. In nonlimiting embodiments ofthe present invention, at least one or both of substrates 20 and 30 aremade of glass, for example, float glass. Moreover, first substrate 20and second substrate 30 are both transparent. In addition, but notrequired, one or both of substrates 20 and 30 can be colored or tinted.In one nonlimiting embodiment of the present invention, each of thetransparent substrates and coatings incorporated into the aircraftwindow assembly 10 has a luminous transmittance of at least 70%. As usedherein, the terms “luminous transmittance” and “light transmittance”mean the measure of the total amount of visible light transmittedthrough a transparency. The luminous transmittance data provided in thisspecification is measured for CIE standard illuminant A and indicted asLTA.

[0029] First substrate 20 and second substrate 30 are spaced apart andin a substantially parallel facing relationship with respect to eachother, defining a chamber 41 therebetween. Such a relationship can beachieved through spacing element 45. Spacing element 45 can bepositioned in any manner capable of maintaining desired spacing betweenfirst substrate 20 and second substrate 30. In one nonlimitingembodiment of the invention, spacing element 45 extends about theperimeter of electrochromic window assembly 10 adjacent the outer edgesof first substrate 20 and second substrate 30 in a sealing manner, as isknown in the art. Although not required, spacing element 45 can bepositioned slightly inward from the outer edges of first substrate 20and second substrate 30. Such positioning provides a slight overhang ofthe first and second substrates, which can expose a portion of first andsecond coatings 29 and 39, discussed below, for improved electricalcontact. Spacing element 45 can be constructed of any nonelectricallyconductive material. In one nonlimiting embodiment of the invention,element 45 is a polymeric material, e.g. curable organic polymericmaterials, such as but not limited to a thermoplastic material,thermosetting material, UV curing resin material, and combinationsthereof. Epoxy based organic sealing materials are useful as sealingelement 45.

[0030] The perimeter of first substrate 20 defines opposing ends 20 aand 20 c, which are opposite each other, as well as opposing ends 20 band 20 d, which are opposite each other. Similarly, second substrate 30includes opposing ends 30 a and 30 c, as well as opposing ends 30 b and30 d.

[0031] First substrate 20 and second substrate 30 are each provided witha layer of a transparent electrically conductive material in the form offirst conductive coating 29 and second conductive coating 39,respectively, on facing major surfaces 21 and 31, respectively, of thesubstrates. First and second conductive coatings 29 and 39 can be anymaterial that is substantially transparent to visible light, bonds wellto the substrate surfaces, is resistant to corrosion by any materialswithin the electrochromic device as well as the atmosphere, and has goodelectrical conductance. Although not required, coatings 29 and 39typically include one or more metal or metal oxide coatings such as butnot limited to silver, gold, tin oxide, indium tin oxide (ITO), fluorinedoped tin oxide (FTO), antimony doped tin oxide, ITO/metal/ITO (IMI), aswell as any other materials known in the art. Conductive coatings 29 and39 can be applied by any of several well known methods, includingpyrolysis, chemical vapor deposition and magnetron sputtering. First andsecond conductive coatings 29 and 39 can be constructed from the same ordifferent materials. Without limiting the present invention, coatingsuseful in the present invention include an electrically conductivefluorine doped tin oxide coated glass available from PPG Industries,Inc. of Pittsburgh, Pennsylvania and marketed under the trademark“NESA®”, and an electrically conductive indium tin oxide coated glassavailable from PPG Industries, Inc. and marketed under the trademark“NESATRON®”.

[0032] In one nonlimiting embodiment of the invention, first and secondconductive coatings 29 and 39 have a sheet resistance ranging from 1 to10 ohms per square, e.g. ranging from 2 to 5 ohms per square. Further,the thickness of first and second conductive coatings 29 and 39 can bethe same or different relative to each other and the coating thicknesscan be uniform, i.e. the same general thickness throughout, ornonuniform, i.e. the coating thickness varies. In one nonlimitingembodiment of the present invention, the coatings have the samegenerally uniform thickness, ranging from 5,000 Å to 50,000 Å, e.g. from13,000 Å to 26,000 Å.

[0033] Electrochromic medium 40 is contained within the chamber 41formed between first substrate 20 and second substrate 30.Electrochromic medium 40 can be any type of material as is known in theart, and can be in any known form, such as but not limited toelectrochromic solutions, gels, semi-solid materials, and the like.Electrochromic medium 40 includes at least one electrochromic compoundor dye that defines a color. Such materials are well known in the art tocolor to successively darker colors or shades as a larger electricalpotential is applied. When the potential is turned off or reversed, thecoloring is removed or bleached, allowing full transmittance of lightthrough electrochromic medium 40.

[0034] In one nonlimiting embodiment of the present invention,electrochromic medium 40 is a solution-phase type electrochromic medium,in which a material contained in solution in an ionically conductingelectrolyte remains in solution in the electrolyte whenelectrochemically reduced or oxidized (including a gel). In anothernonlimiting embodiment of the present invention, electrochromic medium40 is a surface-confined electrochromic medium, in which a material thatis attached directly to an electronically conducting electrode orconfined in close proximity thereto remains attached or confined whenelectrochemically reduced or oxidized. In still another nonlimitingembodiment of the present invention, electrochromic medium 40 is anelectrodeposition-type electrochromic medium, in which a materialcontained in solution in the ionically conducting electrolyte forms alayer on the electronically conducting electrode when electrochemicallyreduced or oxidized.

[0035] Although not required, in one embodiment, electrochromic medium40 includes at least one anodic electrochromic compound and at least onecathodic electrochromic compound, with the anodic compound representingan oxidizable material and the cathodic compound representing areducible material. Upon application of electrical potential to theelectrochromic medium, the anodic electrochromic compound oxidizes andthe cathodic electrochromic compound simultaneously reduces. Suchsimultaneous oxidation and reduction results in a change in theabsorption coefficient of at least one wavelength in the visiblespectrum. The combination of such anodic and cathodic electrochromiccompounds in electrochromic medium 40 defines the color associatedtherewith upon application of an electrical potential. Such cathodicelectrochromic compounds are commonly referred to as viologen dyes, andsuch anodic electrochromic compounds are commonly referred to asphenazine dyes.

[0036] Electrochromic medium 40 can also include other materials such assolvents, light absorbers, light stabilizers, thermal stabilizers,antioxidants, thickeners, viscosity modifiers and similar materials.

[0037] Although not required, in one nonlimiting embodiment of theinvention, at least one edge of coating 29 and/or 39 extend at least inclose proximity to an edge of the substrate 20 and/or 30, respectively,i.e. to the perimeter edge 11 of assembly 10, e.g. within 2 inches, or 1inch or 0.5 inches (5.08 cm, or 2.54 cm or 1.27 cm) of the perimeteredge 11. In the particular nonlimiting embodiment of the invention shownin FIGS. 1-3, the all the edges of coatings 29 and 39 extend at least inclose proximity to the perimeter edge 11 of assembly 20, and in onenonlimiting embodiment, all the edges of coating 29 and 39 extend to theedge of their corresponding substrate and thus to the perimeter edge 11of assembly 10. A plurality of first spaced facilities contacts firstconductive coating 29, and a plurality of second facilities contactsecond conductive coating 39. In one nonlimiting embodiment of thepresent invention, the plurality of first spaced comprises a pluralityof bus bars 60, and the plurality of second facilities comprise aplurality of bus bars 80. Without limiting the present invention, in oneparticular embodiment, bus bars 60 are anodic bus bars while bus bars 80are cathodic bus bars. Such bus bars 60 and 80 provide electricalconnection between a DC power source (not shown in FIGS. 1-3) and firstand second conductive coatings 29 and 39, respectively. Such electricalconnection can be established in any known manner. For example, each ofanodic bus bars 60 can be connected to an anodic conductive wire 65 bysolder joint 64, while each of cathodic bus bars 80 can be connected toa cathodic conductive wire 85 by solder joint 84, as shown in FIG. 3. Inthis manner, a positive current is applied to the anodic bus bars 60 anda negative current is applied to the cathodic bus bars 80, producing anelectrical potential therebetween within the electrochromic cell.Further, an external cover or insulator (not shown) can be providedabout the perimeter edge 11 of electrochromic window assembly 10 toprotect spacing assemblies 45, wires 65 and 85 and/or joints 64 and 84.

[0038] In the particular embodiment of the invention shown in FIGS. 1-3,the edges of coating 29 extend to the perimeter edge 11 of assembly 10and anodic bus bars 60, which are in contact with first conductivecoating 29, are provided along opposing ends 20 a and 20 c of firstsubstrate 20. In this manner, electrical current from the power sourceis provided to the opposing edges of the first conductive coating 29along opposing ends 20 a and 20 c of first substrate 20. Similarly, theedges of coating 39 extend to the perimeter edge 11 of assembly 10 andcathodic bus bars 80, which are in contact with second conductivecoating 39, are provided along opposing ends 30 b and 30 d of secondsubstrate 30. In this manner, electrical current from the power sourceis provided to the opposing edges of the second conductive coating 39along opposing ends 30 b and 30 d of second substrate 30. Furthermore,these opposing ends of first and second coatings 29 and 39 to which theelectrical current is applied are spaced from each other. Withoutwishing to be bound by any particular theory, it is believed that byapplying the current to opposite ends of the coatings and spacing theends of a first coating that are energized with a positive current fromthe ends of a second coating that are energized by a negative currentresults in a uniform application of electrical potential throughout theentire electrochromic cell, resulting in uniform coloring of theelectrochromic medium and reducing the iris effect. As used herein, theterm “uniform coloring” means that those portions of the electrochromicmedium that change color due to the applied electrical potential, allchange generally in the same manner, e.g. generally at the same timeand/or generally at the same rate.

[0039] In another nonlimiting embodiment of the present invention, busbars 60 are arranged along opposing edges 20 a and 20 c as well as alongopposing edges 20 b and 20 d, and bus bars 80 are arranged alongopposing edges 30 b and 30 d as well as along opposing edges 30 a and 30c. In this manner, the anodic bus bars 60 are provided about theperimeter of the entire first substrate 20 and the cathodic bus bars 80are provided about the perimeter of the entire second substrate 30, i.e.bus bars 60 and 80 are positioned about the entire perimeter edge 11 ofassembly 10. In one particular nonlimiting embodiment shown in FIGS.1-3, bus bars 60 and bus bars 80 are arranged in alternating fashion,i.e. each bus bar 60 is arranged between each bus bar 80 about theperimeter edge 11 of window assembly 10. Such an arrangement providesuniform application of electrical potential through the entireelectrochromic window assembly 10. Although not required, in onenonlimiting embodiment of the invention, each anodic bus bar 60 isspaced from each cathodic bus bar 80 along the perimeter edge 11 of thewindow assembly 10 a distance of at least 0.5 inches (1.27 cm). Suchspacing ensures that the current between the bus bars will not short andprovides uniform electrical potential through the entire electrochromicdevice. In addition, this bus bar configuration provides that even underprolonged application of an electrical potential, dye segregation isminimized. Dye segregation is the tendency of the dyes to migrate towardand concentrate at the portion of the assembly where the electricalpower is the greatest, typically along the bus bars.

[0040] Bus bars 60 and 80 can be made of any highly conductive materialtypically used for bus bars and well known in the art. Nonlimitingexamples of typical bus bar materials include metal foil, e.g. copperfoil, metal coating, e.g. gold coatings, and conductive metal containingceramic paints, e.g. silver ceramic paint.

[0041] The size and shape of bus bars 60 and 80 can be tailored to theparticular geometry of the electrochromic window assembly. In onenonlimiting embodiment of the present invention, each of bus bars 60 and80 are at least 0.5 inches (1.27 cm) in length.

[0042] As indicated, electrochromic medium 40 is capable of changing itscolor and thus its light transmittance when an electrical potential isapplied through the medium. Application of the electrical potential canbe selective, i.e. the electrochromic window assembly is switchablebetween one level of transmittance, when no electrical potential isapplied, and a second level of transmittance, when electrical potentialis applied to change the color of the dyes and reduce the luminoustransmittance of the electrochromic medium 40. This feature is mosteasily accomplished by providing a switch for selectively applyingelectrical current to the window assembly.

[0043] In one nonlimiting embodiment of the present invention, thecoloring of the electrochromic medium between the energized andnon-energized electrical states is self-erasable, i.e. the coloring ofthe electrochromic medium when in an electrochemically activated stateupon application of an electrical potential, automatically returns orerases to its original state, e.g. colorless state, when the electricalpotential is removed. In should be appreciated that the original statecan be a colorless state or it can have a color or tint.

[0044] In a further nonlimiting embodiment, the electrochromic windowassembly is switchable and non-self-erasing, i.e. application of theelectrical potential causes the electrochromic medium to color, and theelectrochromic medium will remain in the colored state until theelectrical potential is reversed or shorted.

[0045] Moreover, the color of the dye can be of a constant darkness orshade upon application of an electrical potential, or it can be ofvarying degrees of darkness or shading depending upon the magnitude ofthe electrical potential established through the electrochromic medium.For example and without limiting the present invention, specificcoloring or shading of the coloring can be varied over a range ofvoltages and power densities. Upon application of a low power density tothe electrochromic medium, the dye can begin to color. Increasing thevoltage can cause the color of the dye to darken to a deeper shade orintensity. In this manner, the window assembly can include varyingdegrees of light transmittance upon varying of the electrical potential.The window assembly can, therefore, be adjusted to a desired level ofdarkness or shading based upon the amount of electrical potentialapplied thereto. This can be easily accomplished, for example, byincorporating a switch or some other control between the electricalpower source and the window assembly, as will be discussed later in moredetail. Although not required, in one nonlimiting embodiment of thepresent invention, the electrochromic window assembly is switchablebetween a minimum LTA value ranging from 1 to 20 percent and a maximumLTA value ranging from 60 to 80 percent. As such, the electrochromicwindow assembly can effectively function as an opaque shade for a windowwhen desired.

[0046] An alternate nonlimiting embodiment is shown in FIGS. 4 and 5. Inthis particular embodiment, electrochromic window assembly 110 is in theform of a generally oval shaped window, which can be used, for example,as an aircraft cabin window. Although not required, in this particularembodiment of the invention, the oval shaped window has a symmetricalgeometry, as with the embodiment described above. In a similar manner,electrochromic window assembly 110 includes spaced apart first substrate120 and second substrate 130, as well as first conductive coating 129,second conductive coating 139 and electrochromic medium 140therebetween. Coatings 129 and 139 are applied to opposing facingsurfaces of substrates 120 and 130, respectively, and electrochromicmedium 140 is positioned between the coatings. Substrates 120 and 130are separated by spacer 145.

[0047] Bus bar 160 a is connected to an edge of first conductive coating129 along first end 120 a of first substrate 120, and bus bar 160 c isconnected to an opposing edge of first conductive coating 129 alongopposing second end 120 c of first substrate 120. Further, bus bar 180 bis connected to an edge of second conductive coating 139 along first end130 b of second substrate 130, and bus bar 180 d is connected to anopposing edge of second conductive coating 139 along opposing second end130 d of second substrate 130. Although not required, in one nonlimitingembodiment of the invention, bus bars 160 a and 160 c are anodic busbars, while bus bars 180 b and 180 b are cathodic bus bars. Applicationof electrical current to opposing ends of coating 129 through bus bars160 a and 160 c, and to opposing ends of coating 139 through bus bars180 b and 180 d, and spacing the energized opposing ends of coating 129from the energized opposing ends if coating 139 generates an electricalpotential through the electrochromic medium 140 and causes theelectrochromic medium 140 to change color in a uniform manner.

[0048] In the embodiment depicted in FIGS. 4 and 5, the size and shapeof bus bars 160 and 180 are longer in length relative to the busarrangement of FIG. 1. Although not required, in one nonlimitingembodiment of the present invention, each of bus bars 160 and 180 areequal in length, and bus bars 160 and 180 are spaced about the perimeteredge of the assembly 110 at least 0.5 inches (1.27 cm) apart.

[0049]FIGS. 6 and 7 shown a nonlimiting electrochromic window assembly210 having a generally symmetrical rectangular geometry. Such anassembly can be useful, for example, as an automobile windshield, rearwindow or sunroof, or as an architectural glazing. In a similar manneras the previous embodiments, electrochromic window assembly 210 includesspaced apart first substrate 220 and second substrate 230, as well asfirst conductive coating 229, second conductive coating 239 andelectrochromic medium 240. Coatings 229 and 239 are applied to opposingfacing surfaces of substrates 220 and 230, respectively andelectrochromic medium 240 is positioned between the coatings. Substrates220 and 230 are separated by spacer 245.

[0050] Assembly 210 further includes bus bars 260 and 280. Although notrequired, in this particular embodiment of the invention, bus bars 260are anodic bus bars and bus bars 280 are cathodic bus bars. Anodic busbars 260 a and 260 b are connected to a first edge of first conductivecoating 229 along first end 220 a of first substrate 220, and bus bars260 c and 260 d are connected to an opposing edge of first conductivecoating 229 along opposing second end 220 c of first substrate 220.Further, cathodic bus bar 280 a is connected to a first edge of secondconductive coating 239 along first end 230 a of second substrate 230 ata position spaced between anodic bus bars 260 a and 260 b, and cathodicbus bar 280 b is connected to a second opposing edge of secondconductive coating 239 along opposing second end 230 c of secondsubstrate 230 at a position spaced between anodic bus bars 260 c and 260d. Further, bus bars 280 c and 280 d are connected to a third edge ofsecond conductive coating 239 at third end 230 b of second substrate230, and bus bars 280 e and 280 f are connected to a fourth opposingedge of second conductive coating 239 at opposing fourth end 230 d ofsecond substrate 230. Application of electrical current to opposing endsof coating 229 through bus bars 260 a, 260 b, 260 c and 260 d, and aboutthe periphery of coating 239 through bus bars 280 a, 280 b, 280 c, 280d, 280 e and 280 f generates an electrical potential through theelectrochromic medium 240 and causes the electrochromic medium 240 tochange color in a uniform manner.

[0051] Although not required, in the particular nonlimiting embodimentof the invention shown in FIGS. 6 and 7, bus bars 260 and 280 are equalin length, and bus bars 260 and 280 are spaced about the perimeter edgeof the assembly 210 at least 0.5 inches (1.27 cm) apart.

[0052] A further nonlimiting embodiment of the present invention isshown in FIGS. 8 and 9, in which electrochromic window assembly 310includes a non-symmetric geometry. While such a non-symmetricalelectrochromic window assembly can be provided for any application, thespecific nonlimiting embodiment shown is in the form of an automobileside window, commonly referred to as a sidelite. Electrochromic windowassembly 310 includes a first portion 301 and a second portion 302. Inuse as an automobile sidelite, first portion 301 represents the portionof the window assembly which is above the door panel of an automotivevehicle and visible when the window is closed, while second portion 302represents the portion of the window assembly that remains below thedoor panel at all times, including when the window is closed, and istherefore not visible. Electrochromic window assembly 310 includesspaced apart first substrate 320 and second substrate 330, as well asfirst conductive coating 329, second conductive coating 339 andelectrochromic medium 340, as with the previously discussed embodiments.Coatings 329 and 339 are applied to opposing facing surfaces ofsubstrates 320 and 330, respectively, and electrochromic medium 340 ispositioned between the coatings. Substrates 320 and 330 are separated byspacer 345.

[0053] Electrochromic assembly 310 includes bus bar 360 aconnected to anedge of first conductive coating 329 along first end 320 a of firstsubstrate 320, and bus bar 360 b connected to first conductive coating329 along a lower portion of first substrate 320 near opposing secondend 320 c. Although bus bar 360 b could be positioned along edge 320 cof substrate 320, in the particular embodiment of the invention shown inFIGS. 8 and 9, bus bar 360 b is not positioned along edge 320 c, forreasons that will be discussed later in more detail. Electrochromicassembly 310 further includes bus bars 380 a and 380 b connected to afirst edge of second conductive coating 339 along first end 330 b ofsecond substrate 330, and bus bars 380 c, 380 d and 380 e connected toan opposing second edge of second conductive coating 339 along opposingsecond end 330 d of second substrate 330. Although not required, in onenonlimiting embodiment, bus bars 360 a and 360 b are anodic bus bars,while bus bars 380 a, 380 b, 380 c, 380 d and 380 e are cathodic busbars. Application of electrical current to coatings 329 and 339 throughbus bars 360 a, 360 b, 380 a, 380 b, 380 c, 380 d and 380 e generates anelectrical potential through the electrochromic medium 340, causing theelectrochromic medium 340 to change color in a uniform manner.

[0054] As noted, electrochromic window assembly 310 includes anon-symmetrical geometry. In particular, the side of window assembly 310formed by first ends 320 b and 330 b of substrates 320 and 330,respectively, is shorter in length than the opposing side of windowassembly 310 formed by second ends 320 d and 330 d. As such, in thisparticular nonlimiting embodiment, the bus bar arrangement is adjustedto compensate for such non-symmetrical shape. For example, with respectto the cathodic bus bar arrangement, two bus bars 380 a and 380 b areprovided in contact with second conductive coating 339 along end 330 b,while three bus bars 380 c, 380 d and 380 e are provided in contact withsecond conductive coating 339 along opposing end 330 d. Further, thelength of these bus bars can be adjusted to provide for an appropriatefitting and geometry, as well as appropriate level of current flow. Suchan arrangement with differing number and differing lengths of bus barscompensates for the current flow across the electrochemical cell due tothe non-symmetrical geometry of the electrochromic window assembly 310.

[0055] In addition, the current applied to the bus bars can be adjustedin order to compensate for the non-symmetrical shape. For example andwithout limiting the present invention, resistors (not shown) can beincorporated into the current flow to bus bars 380 a and 380 b in orderto reduce the amount of current flowing to these bus bars. As such,compensation is provided for the applied potential to thenon-symmetrical assembly. As an alternative, a controller can be used tocontrol the current delivered to each bus bar, as will be discussedlater in more detail.

[0056] With continued reference to FIGS. 8 and 9, while the top edge ofwindow assembly 310, formed by first ends 320 a and 330 a, is uniformand only slightly curved, the opposing edge of window assembly 310,formed by second ends 320 c and 330 c, is entirely non-uniform, havingcurved portions and a straight portion, resulting in a non-symmetricallyshaped window assembly having varying distances between opposing edgesat different portions. As such, arrangement of the bus bars at thisportion of the window assembly is difficult. To compensate for suchnon-symmetric geometry, in the particular embodiment of the inventionshown in FIGS. 8 and 9, a single bus bar 360 b is provided in electricalcontact with first conductive coating 329. Such an internal bus bar 360b can be provided, e.g. by adhesively attaching bus bar 360 b to firstconductive coating 329 with a conductive adhesive along substrate 320. Anonelectrically conductive layer (not shown), such as but not limited toadhesive tape, can be placed over bus bar 360 b to act as an insulator,preventing bus bar 360 b from electrically contacting second conductivecoating 339. Such adhesive tape can further act as a spacer, maintainingappropriate spacing between first substrate 320 and second substrate330. Internal bus bar 360B can be made of the same materials asdiscussed earlier for the other bus bars.

[0057] As a result, in one nonlimiting embodiment of the presentinvention, the electrochromic assembly includes at least one bus barspaced from the edge of the assembly and positioned within the assembly.

[0058] Although not required, in the particular embodiment of theinvention shown in FIGS. 8 and 9, a portion 361 b of internal bus bar360 b extends toward an edge of window 310, for example perpendicularlyas shown in FIGS. 8 and 9 to edge 320 c, to provide external contactwith the conductive wire for electrical connection of the bus bar 360 bwith a power source. Since this internal bus bar arrangement iscontained within portion 302 of window assembly 300, none of thecomponents are visible, as portion 302 is maintained within the doorpanel of the automobile. As an alternative, at least a portion of thebus bar 360 b can be positioned within section 301 of assembly 300.

[0059] With respect to the automobile sidelite shown in FIGS. 8 to 9, itis noted that in an alternative embodiment, the bus bar contacts can beprovided on exterior top and side edges of the window assembly, withseparate contact points provided within the frame of the automobile forestablishing contact with the power source. This arrangement provides anappropriate assembly for automobile windows that are not encased withina door frame, since there is no external cover in such an arrangement toconceal the contacts. Such an arrangement would not be detrimental tothe darkening of the window assembly, since closing the window wouldpermit contact with the power source, and since it would not benecessary to shade the window when the window is open.

[0060] The amount of current applied to the electrochromic windowassembly can be selected based on the specific assembly and the specificelectrochromic medium used. In one nonlimiting embodiment of theinvention, the amount of current applied ranges from 0.4 volts to 1.2volts, e.g. from 0.5 volts to 1.0 volts.

[0061] Use of the electrochromic window assembly will now be described,with specific reference to FIGS. 8 to 9 as exemplary of the presentinvention. Electrochromic window assembly provided as described above,is a generally transparent assembly when no electrical potential isapplied thereto. As such, electrochromic window assembly 310 is in thelightened state and full light transmittance is possible. When darkeningof the window assembly is desired, the electrochromic window assembly isactivated, for example by a switch that is activatable by the user.Activation of the switch causes the power source to supply current tobus bars 360 and 380 in any convenient manner, e.g. through the wireleads attached thereto, and to first and second conductive coatings 329and 339. Such current causes an application of electrical potential tothe electrochromic medium, which in turn causes the at least one anodicelectrochromic compound to oxidize and the at least one cathodicelectrochemical compound to reduce. This reaction results in a change incolor of the electrochromic medium such that the electrochromic mediumbegins to absorb light and darken. Since the electrical potentialbetween coatings 329 and 339 is applied through the bus bar arrangementas set forth above, the coloring of the electrochromic medium is rapidand uniform throughout the entire electrochromic window assembly,without any iris effect or gradual change in color.

[0062] Deactivation of the assembly 310 causes the supply of power to beinterrupted to bus bars 360 and 380. As such, the potential beingapplied to electrochromic medium 340 is removed. Such deactivation canbe affected using the same switch arrangement as discussed above toactivate the assembly 310. As discussed earlier, in the case of aself-erasing electrochromic medium, the window assembly 310 will returnto its original state. In the case of a non-self-erasing electrochromicmedium, the color will remain until the electrical potential through themedium is reversed.

[0063] In a further embodiment of the present invention, only a portionof the electrochromic window assembly can be colored to establish apartially shaded window. Such partial shading can be achieved byselectively applying current to a selected number of the anodic bus barsand cathodic bus bars, thereby creating the electrical potential throughonly a portion of the electrochromic window assembly. For example, whensuch a window assembly 310 is in the form of an automobile sidelite, itcan be desirable to create a darkened or shaded top area of the sidelitein order to reduce the level of sunlight transmitted therethrough, whilemaintaining a lightened state at the middle and bottom areas of thesidelite to maintain a high level of light transmittance therethrough,for example to more easily view the side-view mirrors. In the particularembodiment of the invention shown in FIGS. 8 and 9, such preferentialarea shading can be accomplished, for example, by applying current onlyto anodic bus bar 360 a and cathodic bus bars 380 a and 380 c, as willbe discussed later in more detail. Such selective application of currentestablishes an electrical potential at only a selected portion ofelectrochromic window assembly 310, and in this particular embodiment,along the top area portion of assembly 310. As such, only a portion ofthe electrochromic medium between these areas of current applicationwill change color, resulting in a partially shaded assembly, i.e. theluminous transmittance through the portion of the electrochromic mediumbetween the energized portions of the coatings (due to selectivepowering of the bus bars) will change as compared to those portions ofthe electrochromic medium that are not between the energized portions ofthe coatings.

[0064] It is noted that prolonged application of electrical current to aselected number of facilities in this manner can result in “bleeding” ofthe electrochromic medium, in which the electrochromic medium in theareas of the electrochromic window assembly to which electrical currentis not applied gradually begins to color to a darkened state. This isbelieved to be due to the current flowing through the entire conductivelayer even though the electrical current is only applied to a portion ofthe conductive layer, thus enlarging the area of the electrochromicmedium through which the electrical potential is applied. The amount ofbleeding is based on the specific sheet resistance of the conductivecoatings. For example, incorporating conductive coatings having a highersheet resistance will reduce this bleeding effect somewhat. Increasedsheet resistance will, however, consume more power to switch the colorof the device, and will take a longer period of time to achieve fullcoloring and switching of the device.

[0065] In order to avoid this bleeding effect, particularly with lowsheet resistance conductive coatings, it is possible to ground or shortthe current at the facilities which are not selected for application ofelectrical current to create the shaded area. For example and asdiscussed above, in FIGS. 8 and 9, the partially shaded window assemblycan be achieved by selectively applying current to anodic bus bar 360 aand cathodic bus bars 380 a and 380 c. By grounding or shorting thecurrent at the remaining bus bars, namely anodic bus bar 360 b andcathodic bus bars 380 b, 380 d and 380 e, no electrical potential isapplied to the bottom area of electrochromic window assembly 310. Thus,the color of electrochromic medium 340 at the bottom portion of assembly310 is generally maintained in a lightened state, and any bleedingeffect of coloring from the top portion which is colored due toapplication of electrical potential is reduced.

[0066] Still further, the electrochromic window assembly can include agradient shading across the surface thereof, such that electrochromicwindow assembly gradually changes from a lightened state, throughsuccessively darker shaded sections to a darkened state. This can beaccomplished in a similar manner as described above with respect to thepreferentially shaded area, by applying varying voltages to differentfacilities in order to achieve varying degrees of darkening of theelectrochromic medium. For example and with further reference to FIGS. 8and 9, to achieve a graded shading effect in one nonlimiting embodimentof the invention, a voltage of 0.7 volts can be applied to bus bars 360a, 380 a and 380 c and a decreased voltage of 0.4 volts can be appliedto bus bars 380 b and 380 d. Although not required, the electricalcurrent can further be grounded or shorted to bus bars 360 b and 380 e.As such, electrochromic window assembly 300 can be gradually shaded froma darkened state at the top portion, through a slightly darkened stateat the middle portion to a lightened state at the bottom portion.

[0067] In another nonlimiting embodiment of the present invention, it ispossible to achieve a gradient shading across the electrochromic windowassembly, such that a portion of the electrochromic window assembly isfully colored, while a separate portion of the electrochromic windowassembly is only partially colored. For example and without limiting thepresent invention, a voltage of 0.7 volts can be applied to bus bars 360a, 380 a and 380 c while a voltage of 0.4 volts is applied to bus bars360 b, 380 b, 380 d and 380 e. As such, electrochromic window assembly310 will include a gradient shading from a completely darkened state atthe top portion, through a slightly darkened state at the bottomportion.

[0068] It is noted that while such preferential shading and/or gradualgradient shading of the electrochromic window assembly has beendiscussed with particular reference to the geometry of FIGS. 8 and 9 andreferring to an automobile sidelite, it is contemplated that suchshading or gradient shading can be accomplished with any electrochromicwindow assembly, such as but not limited to, the specific assembliesshown and discussed above. For example, in one particular, nonlimitingembodiment, the electrochromic window assembly is an automobilewindshield, with the portion of the assembly that is selectively coloredbeing the upper edge portion of the windshield, which typicallycorresponds to the shade band. With reference to FIGS. 6 and 7, this canbe accomplished, for example, through application of an electricalcurrent to bus bars 260 a, 260 b, 280 a, 280 c, and 280 e, whileshorting bus bars 260 c, 260 d, 280 b, 280 d, and 280 f. This will causea top portion of electrochromic window assembly 200 to darken and thebottom portion to remain in a lightened state.

[0069] In a further embodiment, the electrochromic window assembly canbe an automobile sunroof, with one side of the assembly beingselectively colored. With reference to FIGS. 6 and 7, this can beaccomplished, for example, through application of an electrical currentto bus bars 260 a, 260 c, 280 c, and 280 d, while shorting bus bars 260b, 260 d, 280 a, 280 b, 280 e, and 280 f, causing one side portion ofelectrochromic window assembly 200 to darken and the other side portionto remain in a lightened state.

[0070] It shown be appreciated that due to the multiple anodic andcathodic bus bars positioned about the perimeter edge 11 of windowassembly 10 as shown in FIG. 1 and discussed in detail above, thisembodiment can also be operated in a manner that darkens one or moreselected portions of assembly 10 and/or produces a gradient shading inone or more selected portions of assembly 10.

[0071] In order to control the darkening pattern of the electrochromicwindow assemblies of the types disclosed herein, a controller can beused to control power distribution to the conductive coatings. Forexample and referring to FIG. 10, a controller 390 can be used tocontrol the electrical power supplied to each bus bar in assembly 310 bya DC power source 391. More particularly, controller 390 can controlwhether a particular bus bar is energized (i.e. current is delivered tothe bus bar), not energized or shorted. In addition, controller 390 cancontrol how much current is delivered to the particular bus bar. Bycontrolling where and how much current should be supped to the coatings,the controller 390 can establish an electrical potential through only aselected portion of the electrochromic medium such that its luminoustransmittance through the selected portion is different from itsluminous transmittance through its other portions. As a result, thecontroller 390 can be used to produce a desired change in the luminoustransmittance of the assembly, such as but not limited to, darkening aselected portion of the assembly or providing a gradient shading asdiscussed earlier. The controller 390 can also control the current asrequired to account for non-symmetrical features of the assembly, e.g.shape, bus bar length, coating thickness, etc.

[0072] The features and advantages of the present invention will befurther described and understood through the following examples, whichare not to be construed as limiting the scope of the invention.

EXAMPLE

[0073] An electrochromic window assembly 410 in the form of anautomobile side window or sidelite was constructed as follows. A firstglass substrate 420 having a geometry as shown in FIG. 11, with anoverall size of approximately 23 inches (58.42 cm) in width and 21inches (53.34 cm) in length, and has a thickness of approximately 80mils (2.03 mm), was provided. This first substrate 420 was coated on onesurface with a coating 429 of ITO using magnetic sputter vapordeposition (MSVD) techniques which are well known in the art to providea conductive layer. The resistance of the conductive coating 429 was 2ohms per square and the conductive coating was applied to a thickness of25,000 Å. A second glass substrate 430 similar to that of the firstglass substrate 420 was provided with a conductive coating 439 in asimilar manner, with the conductive coating 439 being applied to asurface of the second substrate 430 facing the coated surface of thefirst glass substrate 420.

[0074] Anodic bus bars were provided on opposing edges of the firstconductive coating 429. More particularly, a first pair of anodic busbars 460 a and 460 b was provided across the top edge of the firstsubstrate 420 using 3 mil thick copper foil strips that were secured tothe first conductive coating 429 by a conductive adhesive. A portion ofeach strip was laminated within assembly 410 and the remainder of eachstrip was wrapped around the edge of the first substrate 420. Bus bars460 a and 460 b were 10.5 inches and 10.25 inches (26.67 cm and 26.04cm) in length, respectively, and were separated by 0.5 inches (1.27 cm).A third anodic bus bar 460 c was provided by way of a separate strip of3 mil thick copper adhesively attached across a lower portion of thefirst substrate 420 directly on the first conductive coating 429, with afurther strip 461 c of copper also adhesively attached directly on thefirst conductive coating perpendicular to and in contact with bus bar460 c, and extending to the edge of the window assembly 410. Adhesivetape was provided as insulation over bus bars 460 c and strip 461 c. Busbar 460 c was 20.5 inches (52.07 cm) long.

[0075] Four cathodic bus bars were provided on opposing edges of thesecond substrate 430 in contact with the second conductive coating 439.More particularly, cathodic bus bars 480 a and 480 b in the form of twoseparate copper strips spaced 0.5 inches (1.27 cm) from each other andacross one side edge of the second substrate 430 were provided incontact with a first edge of the second conductive coating 439, andcathodic bus bars 480 c and 480 d in the form of two additional separatecopper strips spaced 0.5 inches (1.27 cm) from each other and across theopposite side edge of the second substrate 430 were provided in contactwith an opposing edge of the second conductive coating 439. Each of thebus bars were made of 3 mil thick copper foil and secured to therespective conductive coating by a conductive adhesive. A portion ofeach strip was laminated within assembly 410, and the remainder of eachstrip was wrapped around the edge of second substrate 430. Bus bars 480a, 480 b, 480 c and 480 d were 4.25 inches, 7.25 inches, 4.25 inches and11.75 inches (10.80 cm, 18.42 cm, 10.80 cm and 29.85 cm) in length,respectively

[0076] The two glass substrates 420 and 430 were spaced apartapproximately 24 mils (0.61 mm), with the conductive coatings 429 and439 facing each other. A polymeric resin was applied between the twosubstrates around the perimeter of the assembly to act as a spacer. Anelectrochromic medium 440, including a viologen dye and a phenazine dye,capable of coloring upon application of electrical potential thereto wasinjected between the two substrates. The luminous transmittance (LTA)through the electrochromic window assembly 410 in an uncharged state,i.e. when no current was applied, was approximately 54%.

[0077] The anodic and the cathodic bus bars were connected to a DC powersource through wire leads. Various levels of current were applied todifferent sets of bus bars, as set forth below. Because the edge of theassembly 410 along bus bars 480 a and 480 b is shorter than the opposingedge of the assembly, 0.5 ohm resistors were inserted in line with busbars 480 a and 480 b to vary the current and provide a generally uniformpower density. TABLE I Anodic Bus Bars Cathodic Bus Bars % LTA % LTA Ex.Volts Amps 460a 460b 460c 480a 480b 480c 480d top bottom 1 0.70 0.092(+) (+) (+) (−) (−) (−) (−) <1  2 2 0.70 0.065 (+) (+) Off (−) Off (−)Off <1 6-7 3 0.70 0.154 (+) (+) Short (−) Short (−) Short 14 54 4 0.800.187 (+) (+) Short (−) Short (−) Short 3 54

[0078] In Example 1, current was applied to all of the anodic andcathodic bus bars at 0.70 volts, and therefore, to the entireelectrochromic window assembly 410 with electrical potential evenlydistributed throughout the entire assembly. After 5 minutes, theelectrochromic window assembly achieved a constant or steady state at0.092 amps, in which all of the oxidation/reduction reaction hadoccurred between the anodic and cathodic dye within the electrochromicmedium. As can be seen in Table I, the entire electrochromic windowassembly achieved an excellent coloring, with the top portion of thewindow assembly having and LTA of <1%, and the bottom portion of theassembly having an LTA of approximately 2%. Thus, the coloring ordarkening of the window assembly was achieved quickly and uniformly.

[0079] In Example 2, current was applied to only the anodic and cathodicbus bars arranged at the top of the window assembly 410, specificallyanodic bus bar 460 a and 460 b, and cathodic bus bars 480 a and 480 c,at 0.70 volts. After 5 minutes, the electrochromic window assemblyachieved a constant or steady state at 0.065 amps, in which all of theoxidation/reduction reaction had occurred between the anodic andcathodic dye within the electrochromic medium. As can be seen in TableI, the top portion of the electrochromic window assembly achieved anexcellent coloring, having an LTA of <1%. The bottom portion of theassembly had an LTA of approximately 6-7%. Thus, the coloring ordarkening of the window assembly was non-uniform and had a gradient asviewed from the top to the bottom portion.

[0080] In Example 3, current was applied to only the anodic and cathodicbus bars arranged at the top of the window assembly 410, specificallyanodic bus bar 460 a and 460 b and cathodic bus bars 480 a and 480 c, at0.70 volts. Further, current to the remaining anodic and cathodic busbars, namely anodic bus bar 460 c and cathodic bus bars 480 b and 480 dwas shorted, i.e. any current reaching these bus bars from the energizedbus bars through the conductive coatings was removed. After 5 minutes,the electrochromic window assembly achieved a constant or steady stateat 0.154 amps, in which all of the oxidation/reduction reaction hadoccurred between the anodic and cathodic dye within the electrochromicmedium. As can be seen in Table I, the top portion of the electrochromicwindow assembly achieved partial coloring, having an LTA of 14%. Thebottom portion of the assembly had an LTA of approximately 54%,representing no color change and full transmission through the bottomportion of the assembly. Thus, a partial shade band was achieved acrossthe top of the window assembly, with a small amount of light transmittedthrough the shade band.

[0081] In Example 4, current was applied to only the anodic and cathodicbus bars arranged at the top of the window assembly 410, specificallyanodic bus bar 460 a and 460 b and cathodic bus bars 480 a and 480 c, aswith Example 3, but instead at 0.80 volts. Again, as with Example 3,current to the remaining anodic and cathodic bus bars, namely anodic busbar 460 c and cathodic bus bars 480 b and 480 d was shorted. After 5minutes, the electrochromic window assembly achieved a constant orsteady state at 0.187 amps, in which all of the oxidation/reductionreaction had occurred between the anodic and cathodic dye within theelectrochromic medium. As can be seen in Table I, the top portion of theelectrochromic window assembly achieved excellent coloring, having anLTA of approximately 3%. The bottom portion of the assembly, on theother hand, had an LTA of approximately 54%, representing no colorchange and full transmission through the bottom portion of the assembly.Thus, a complete shade band was achieved across the top of the windowassembly.

[0082] Example embodiments of the present invention have now beendescribed. It will be appreciated that these examples are merelyillustrative of the invention. Many variations and modifications of theinvention will be apparent to those skilled in the art are intended tobe included within the scope of the following claims.

What is claimed is:
 26. A method for providing uniform coloring to anelectrochromic window assembly comprising: providing an electrochromicwindow assembly comprising first and second spaced apart transparentsubstrates defining a chamber therebetween, said first transparentsubstrate having a first conductive coating and said second transparentsubstrate having a second conductive coating, said chamber containing anelectrochromic medium capable of coloring upon application of electricalpotential thereto to provide reduced luminous transmittance; andapplying an electrical current to opposing ends of said first conductivecoating and to opposing ends of said second conductive coating toestablish said electrical potential through said electrochromic medium,said opposing ends of said first conductive coating and said secondconductive coating being spaced from each other, wherein said coloringof said electrochromic medium is uniform.
 27. The method according toclaim 26, wherein said opposing ends of said first conductive coatingand said opposing ends of said second conductive coating are at least inclose proximity to a perimeter edge of said assembly.
 28. The methodaccording to claim 26, further comprising positioning a plurality offirst spaced facilities along opposing ends of said first transparentsubstrate in electrical contact with said opposing ends of said firstcoating for providing said electrical current to said first conductivecoating and positioning a plurality of second spaced facilities alongopposing ends of said second transparent substrate in electrical contactwith said opposing ends of said second coating for providing saidelectrical current to said second conductive coating.
 29. A method forproviding preferential coloring to a portion of an electrochromic windowassembly, comprising: providing an electrochromic window assemblycomprising first and second spaced apart transparent substrates defininga chamber therebetween, said first transparent substrate having a firstconductive coating and said second transparent substrate having a secondconductive coating, said chamber containing an electrochromic mediumcapable of coloring upon application of electrical potential thereto toprovide reduced luminous transmittance; electrically connecting aplurality of first spaced facilities to said first conductive coatingfor providing said electrical potential to said first conductivecoating; electrically connecting a plurality of second spaced facilitiesto said second conductive coating for providing said electricalpotential to said second conductive coating; applying an electricalcurrent to selected ones of said plurality of first spaced facilitiesand to selected ones of said plurality of second spaced facilities toestablish said electrical potential through a selected portion of saidelectrochromic medium such that said selected portion changes color andreduces its luminous transmittance.
 30. The method according to claim29, comprising positioning opposing ends of said first conductivecoating at least in close proximity to a perimeter of said assembly andpositioning opposing ends of said second conductive coating at least inclose proximity to said perimeter of said assembly, electricallyconnecting said plurality of first spaced facilities to said firstconductive coating along said opposing ends of said first conductivecoating, and electrically connecting said plurality of second spacedfacilities to said second conductive coating along said opposing ends ofsaid second conductive coating.
 31. The method according to claim 30,comprising spacing said opposing ends of said first conductive coatingfrom said opposing ends of said second conductive coating along saidperimeter of said assembly.
 32. The method according to claim 29,further comprising shorting said electrical current at other selectedones of said plurality of first spaced facilities and at other selectedones of said plurality of second spaced facilities.
 33. The methodaccording to claim 29, further comprising varying said electricalcurrent applied to said selected ones of said plurality of first spacedfacilities and to said selected ones of said plurality of second spacedfacilities, to provide varying degrees of reduced luminous transmittanceto said selected portion of said electrochromic medium.
 34. The methodaccording to claim 33, wherein said electrochromic window assembly is anautomotive windshield and said portion of said electrochromic medium isa shade band.
 35. The method according to claim 29, comprisingpositioning said first conductive coating at least in close proximity toa perimeter of said assembly and positioning said second conductivecoating at least in close proximity to said perimeter edge of saidassembly, electrically connecting said plurality of first spacedfacilities to said first conductive coating about said entire perimeter,and electrically connecting said plurality of second spaced facilitiesto said second conductive coating about said entire perimeter
 36. Themethod according to claim 35, comprising spacing said plurality of firstspaced facilities at least 0.5 inches apart about said perimeter,spacing said plurality of second spaced facilities at least 0.5 inchesapart about said perimeter, and spacing said plurality of first spacedfacilities from said plurality of second spaced facilities at least 0.5inches about said perimeter.
 37. The method of claim 29, wherein saidfirst and said second conductive coatings, each have a sheet resistanceranging from 1 ohm per square to 10 ohms per square.
 38. The method ofclaim 29, wherein said first and said second conductive coatings, eachhave a thickness ranging from 5,000 Å to 50,000 Å.
 39. The method ofclaim 29, wherein said electrical current is applied to said first andsaid second conductive coatings in the range of 0.5 volts to 1.0 volt.40. The method of claim 33, comprising varying said electrical currentsuch that said luminous transmittance of at least a portion of saidassembly varies from a minimum LTA ranging from 1 to 20 percent and amaximum LTA ranging from 60 to 80 percent.